Thin-film forming method using silane and an oxidizing gas

ABSTRACT

Disclosed is a film-forming method, comprising supplying into a plasma processing chamber at least three kinds of gases including a silicon compound gas, an oxidizing gas, and a rare gas, the percentage of the partial pressure of the rare gas (Pr) based on the total pressure being not smaller than 85%, i.e., 85%≦Pr&lt;100%, and generating a plasma within the plasma processing chamber so as to form a film of silicon oxide on a substrate to be processed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2003-114640, filed Apr. 18, 2003;and No. 2004-095559, filed Mar. 29, 2004, and is a divisional of U.S.application Ser. No. 10/821,843, filed Apr. 12, 2004, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a film used in asemiconductor device such as a semiconductor integrated circuit deviceor a display device such as a liquid crystal display device. The presentinvention also relates to a method of manufacturing a semiconductordevice such as a thin film transistor (TFT) or a metal oxidesemiconductor device (MOS device) and to a semiconductor device. Thepresent invention further relates to a method of manufacturing a displaydevice such as a liquid crystal display device, an organic EL displaydevice or an inorganic EL display device, and to a display device.

2. Description of the Related Art

In general, a silicon oxide film is used as a gate insulating film in asemiconductor device such as a thin film transistor (TFT). A plasma CVD(plasma enhanced chemical vapor deposition) method is known to the artas a method of forming a silicon oxide film under temperatures nothigher than 600° C. so as to prevent adverse effects on the substrate.

In the plasma CVD method, a silicon oxide film is formed as follows. Inthe first step, a monosilane gas is mixed with an oxygen gas, followedby supplying the mixed gas into a chamber in which a substrate isarranged. Under this condition, a plasma is generated within the chamberso as to achieve the plasma discharge of the monosilane gas and theoxygen gas, thereby depositing silicon oxide on the substrate.

The conventional plasma CVD method gives rise to the problem that theoxygen atoms are not supplied sufficiently, with the result that formedis a silicon oxide film having a large oxygen deficiency. Naturally, itis of high importance to overcome the problem.

Also, proposed in patent document e.g., Japanese Patent Disclosure(Kokai) No. 11-279773, is a plasma CVD method using a mixed gasconsisting of two kinds of gases including gaseous molecules and a raregas having appropriate excitation levels relative to the gaseousmolecules.

It should be noted that, in a top gate type TFT used in a displaydevice, silicon oxide is deposited in general by a plasma CVD method ona semiconductor layer processed in the form of an island and having athickness of about 50 nm so as to form a gate insulating film having athickness of 80 to 100 nm.

The scale of the display device has been enlarged, and the displaydevice has been made to perform many functions. In this connection, theTFT has come to be applied to a new display device such as an organic ELdisplay device. Such being the situation, miniaturization of the TFT hascome to be required while improving the device characteristics of theTFT. In order to miniaturize the TFT, the gate insulating film isrequired to be rendered thinner. To be more specific, when it comes to aTFT having a channel length of 1 nm, it is required for the thickness ofthe gate insulating film to be decreased to 30 nm.

When it comes to a top gate type TFT in which a gate insulating film isformed on a semiconductor layer formed in the shape of an island, it isnecessary for the gate insulating film to be formed in a manner to coverthe entire region of the semiconductor layer including the steppedportion formed in the semi-conductor layer. It follows that the currentleakage through the gate insulating film tends to be increased in thestepped portion. It should be also noted that the amount of leak currentwill increase of the gate insulating if the gate insulating film is madeof an oxide silicon film that is as thin as 30 nm.

One approach to solve the above problems is to use a laminated structureof plasma CVD films, as seen in the documents 1 and 2 set forth below.

According to the technology disclosed in document 1 referred to above,it is possible to form a film under the temperature lower than thatrequired in the organometallic gaseous phase growth method whilesuppressing the damage done to the underlayer. In addition, the film canbe formed at a film-forming rate higher than that for the atomic layerdepositing method. However, the zirconium oxide film formed by thetechnology disclosed in document 1 gives rise to the problem that theoxygen deficiency in the formed film is significantly large.

Document 1: M. Goto, et al., “Surface Wave Plasma Oxidation at LowTemperature for Gate Insulator of Poly-Si TFTs”, Dec. 4-6, 2002,[Proceedings of The Ninth International Display Workshops], p 355 to p358.

Document 2: “Formation of Zirconium Oxide Film having High DielectricConstant by Plasma CVD using Organometallic Material as Precursor” byReiji Morioka, et al., p 317 to p 318 of the collection of lecturedocuments of the “20^(th) Plasma Processing Research Meeting” held onJan. 29, 2003 and sponsored by Plasma Electronics Branch of AppliedPhysics Institute (an incorporated body).

As described above, if the thickness of the gate insulating film isdecreased to about 30 nm, it is difficult to obtain sufficient devicecharacteristics. In other words, the decrease in the thickness of thesilicon oxide film is limited. Such being the situation, the metaloxides having a dielectric constant higher than that of silicon oxidesuch as hafnium oxide and zirconium oxide have come to attract attentionas a material of the gate insulating film. In other words, in the caseof using a metal oxide having a high dielectric constant as a materialof a gate insulating film, it is expected that the thickness of the gateinsulating film can be further decreased while maintaining thecapacitance of the gate insulating film equal to that of the gateinsulating film formed of a silicon oxide film.

An organometallic gaseous phase growth method (MOCVD method), asputtering method or an atomic layer depositing method (Atomic LayerDeposition: ALD) as a deposition method of a very thin film are known tothe art as a method of forming a film made of a metal oxide such ashafnium oxide or zirconium oxide.

In the organometallic gaseous phase growth method, a film is grown bydecomposing an organometallic compound gas used as a raw material byusing the substrate heated to 500° C. to 700° C., with the result thatit is difficult to form a metal oxide film on a general type of glasssubstrate or a plastic substrate.

A film can be formed at a relatively low temperature in the case ofemploying the sputtering method. However, since particles running at ahigh speed collide against the substrate in the case of employing thesputtering method, the underlayer film tends to be damaged. It followsthat the metal oxide film formed by the sputtering method has a highinterface state density and, in addition, involves a significant oxygendeficiency. Incidentally, in order to make up for the oxygen deficiencyin the metal oxide film, it is necessary to employ, for example, aplasma processing or an annealing treatment under high temperaturesafter the film formation. It follows that the number of manufacturingprocesses needed in the formation of the metal oxide film is increased,which is disadvantageous.

In the atomic layer depositing method, the atomic layers are depositedone layer at a time and, thus, the film-forming rate is very low. Itfollows that the atomic layer deposition method is not adapted for theformation of a TFT because it is necessary for the gate insulating filmincluded in the TFT to have a thickness of tens of nanometers.

A film-forming method employing a plasma CVD technology using anorganometallic material as a precursor is proposed as another method offorming a metal oxide film. The particular film-forming method issummarized below.

In the first step, tetrapropoxy zirconium (Zr(OC₃H₇)₄) is mixed with anoxygen gas and an argon gas. The ratio of the oxygen gas to the argongas within the mixed gas is 1:5. In other words, the percentage of thepartial pressure of the argon gas based on the total pressure of themixed gas is 80%. Then, the mixed gas is introduced into a chamber inwhich a substrate is arranged. Under this condition, a plasma isgenerated within the chamber so as to achieve a plasma discharge of thetetrapropoxy zirconium and the oxygen gas, thereby depositing zirconiumoxide on the substrate.

In the technology disclosed in document 1 referred to previously, twokinds of gases consisting of gaseous molecules and a rare gas having anappropriate excitation state relative to the gaseous molecules are mixedso as to permit the rare gas to decompose the gaseous molecules into anatomic state. In other words, in the case of forming a silicon oxidefilm, a monosilane gas is mixed with an argon gas so as to generate theatomic silicon and, at the same time, an oxygen gas is mixed with axenon gas so as to generate the atomic oxygen. It follows that, in thetechnology disclosed in document 1, at least two plasma generatingapparatuses are required for forming a silicon oxide film or a metaloxide film. Such being the situation, the manufacturing apparatus isrendered complex and the manufacturing price is increased. In addition,the technology disclosed in patent document 1 gives rise to the problemthat it is impossible to use a gas consisting of an organic siliconcompound such as tetraethoxy silane (TEOS) as gaseous molecules forgenerating the silicon atoms.

Further, document 2 pointed out above refers to, for example, therelationship between the Kr dilution ratio and the film thickness owingto the plasma oxidation and to the relationship between the microwaveoutput and the oxygen atom density. However, document 2 simply refers tothe technology of performing a surface wave plasma oxidation at a lowtemperature for forming a gate insulating film for a TFT, failing torefer to, for example, the film-forming technology as in the presentinvention.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a film-forming methodthat permits forming a film having a low oxygen deficiency, a method ofmanufacturing a semiconductor device, a semiconductor device, a methodof manufacturing a display device, and a display device.

According to a first aspect of the present invention, there is provideda film-forming method, comprising:

supplying into a plasma processing chamber at least three kinds of gasesincluding a silicon compound gas (or an organometallic compound gas), anoxidizing gas, and a rare gas, the percentage of the partial pressure ofthe rare gas (Pr) based on the total pressure of all the gases being notsmaller than 85%, i.e., 85%≦Pr<100%; and

generating a plasma within the plasma processing chamber so as to form afilm of silicon oxide (or metal oxide) on a substrate to be processed.

According to a second aspect of the present invention, there is provideda film-forming method, comprising:

supplying into a plasma processing chamber at least three kinds of gasesincluding a silicon compound gas (or an organometallic compound gas), anoxidizing gas, and a hydrogen gas; and

generating a plasma within the plasma processing chamber so as to form afilm of silicon oxide (or metal oxide) on a substrate to be processed.

According to a third aspect of the present invention, there is provideda semiconductor device, comprising a transistor including at least onefilm selected from the group consisting of the silicon oxide film andthe metal oxide film formed by the film-forming method given above. Thesemiconductor device can be formed as a display device. As a result, thesemiconductor device which has a small current leakage can be obtained.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 schematically shows the construction of a plasma CVD apparatusused in the film-forming method according to each of first to thirdembodiments of the present invention;

FIG. 2 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas contained in a mixed gas and the flatband voltage of the MOS device;

FIG. 3 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas contained in a mixed gas and the electrondensity in the mixed gas;

FIG. 4 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas contained in a mixed gas and the formingrate the SiO₂ film;

FIG. 5 is a graph showing the relationship between the percentage of thepartial pressure of the H₂ gas contained in a mixed gas and the flatband voltage of the MOS device;

FIG. 6 schematically shows the construction of a microwave plasma CVDapparatus free from a magnetic field, which is used in the film-formingmethod according to any of fourth to seventh embodiments of the presentinvention;

FIG. 7 is a graph showing the relationship between the percentage of thepartial pressure of the Ar gas contained in a mixed gas and the electrondensity in the mixed gas;

FIG. 8 is a graph showing the current leakage through a HfO₂ film formedby the conventional film-forming method, through a HfO₂ film formed bythe film-forming method according to a fourth embodiment of the presentinvention, and through a HfO₂ film formed by the film-forming methodaccording to a fifth embodiment of the present invention;

FIG. 9 is a graph showing a carbon atom concentration in an Al₂O₃ filmformed by the conventional method, in an Al₂O₃ film formed by the methodaccording to a sixth embodiment of the present invention, and in anAl₂O₃ film formed by the method according to a seventh embodiment of thepresent invention;

FIG. 10 is a plan view showing the construction of a liquid crystaldisplay device comprising TFTs;

FIG. 11 is a cross sectional view showing the construction of a liquidcrystal display device comprising TFTs; and

FIG. 12 is a graph showing the interface state density in a SiO₂ filmformed by the conventional film-forming method, in an Al₂O₃ film formedby the film-forming method according to the sixth embodiment of thepresent invention, and in a laminate film consisting of the SiO₂ filmformed by the conventional film-forming method and the Al₂O₃ film formedon the SiO₂ film by the film-forming method according to the sixthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail.

Described first is a plasma CVD apparatus (plasma enhanced chemicalvapor deposition system) 10 shown in FIG. 1, which is one of thechemical gaseous phase film-forming apparatuses for working thefilm-forming process. The plasma CVD apparatus 10 shown in FIG. 1 is,for example, a parallel flat plate type plasma CVD apparatus. As shownin FIG. 1, the apparatus 10 comprises, for example, a chamber 11 used asa plasma processing chamber, and a pair parallel flat plate typeelectrodes 12 and 13 arranged to face each other in the chamber 11. Ahigh frequency power supplying circuit, for example, high frequencypower source apparatus 14 for applying high frequency power of 500 W(output power) and 40 MHz (frequency) to electrode 12 is connected tothe electrode (upper electrode) 12 via a matching device 15.

The chamber 11 in which is housed a substrate 1 to be processed is avacuum chamber consisting of, for example, a metal container providing ahermetic inner region. A gas inlet pipe 11 a hermetically penetrates anupper portion of the chamber 11. A tip of the gas inlet pipe 11 a isconnected to a shower electrode, which functions as the upper electrode12 as well. A mixed gas from the shower electrode is uniformly emittedonto the surface of the substrate to be processed. A gas evacuationportion 11 b is formed in a bottom portion of the chamber 11. A mixedgas used as a film-forming process gas is introduced from the gas inletportion 11 a into the chamber 11 through the electrode 12 of a showerelectrode structure as denoted by an arrow A in FIG. 1. A vacuum exhaustsystem (not shown) using, for example, a turbo molecular pump isconnected to the gas evacuation portion 11 b. The chamber 11 isevacuated by operating the vacuum exhaust system until a prescribeddegree of vacuum is reached within the chamber 11.

The output terminal of the high frequency power source apparatus 14 forproducing a high frequency power used for generating a plasma isconnected through the matching device 15 for controlling the load to oneof the pair of electrodes 12 and 13 positioned to face each other. Inthe example shown in the drawing, the output terminal of the highfrequency power source apparatus 14 is connected to one of theelectrodes 12 and 13, e.g., to the upper electrode 12, with the otherelectrode 13 connected to the ground potential point.

A stage for supporting the substrate 1 to be processed is arrangedwithin the chamber 11. In the apparatus shown in the drawing, the lowerelectrode 13 also acts as the stage for supporting the substrate 1. Aheating means (not shown) for heating the substrate 1 to be processedsuch as a heater or a lamp anneal is arranged within the stage(electrode 13).

The plasma CVD apparatus 10 is constructed such that the high frequencypower source apparatus 14 is operated after the chamber 11 is evacuatedso as to apply a high frequency power between the electrodes 12 and 13through the matching device 15. Under this condition, a process gas issupplied into the chamber 11 so as to produce a plasma within thechamber 11. A heater is provided for the gas inlet pipe 11 a or the wallof the chamber 11 in case of need. The temperature of the heater iscontrolled so as not to form a film on the gas inlet pipe 11 a or thewall of the chamber 11.

The film-forming method using the apparatus shown in FIG. 1 will now bedescribed.

First Embodiment

In the first step, a substrate 1 to be processed is prepared. Thesubstrate 1 to be processed includes, for example, a silicon substratefor manufacturing a semiconductor device, a glass substrate for forminga display circuit of a liquid crystal display device, or a plasticsubstrate. In the first embodiment, the substrate to be processed isformed of, for example, a silicon substrate.

In the next step, prepared is a mixed gas consisting of at least threekinds of gases including a silicon compound gas formed of a compoundhaving silicon (Si) atoms, an oxidizing gas, and a rare gas.Incidentally, it is possible to mix the silicon compound gas, theoxidizing gas and the rare gas in the process of introducing these gasesinto the chamber 1 so as to form the desired mixed gas.

In the first embodiment of the present invention, the mixed gas isprepared by mixing a tetraethoxy silane (Si(OCH₂CH₃)₄: tetra ethyl orthosilicate) gas, i.e., TEOS gas, used as a silicon compound gas or anorganometallic compound gas, an oxygen gas (O₂ gas) used as an oxidizinggas, and a xenon gas (Xe gas) used as a rare gas. The mixing ratio ofthe TEOS gas to the O₂ gas in the mixed gas is 1:5. Where the totalpressure of the mixed gas is set at 100%, the percentage (diluting rate)of the partial pressure of the Xe gas (Pr) is set at a level not smallerthan 85%, i.e., 85%≦Pr<100%. For example, the percentage Pr noted aboveis set at 90%.

In the next step, the substrate 1 to be processed is housed in thechamber 11 of the plasma CVD apparatus 10 shown in FIG. 1, followed byoperating the vacuum exhaust system so as to establish a substantiallyvacuum condition reaching a prescribed degree of vacuum within thechamber 11. After the chamber 11 is evacuated so as to establish thesubstantially vacuum condition, the mixed gas is supplied through thegas inlet portion 11 a into the chamber 11 until the gaseous pressurewithin the chamber 11 is increased to reach 60 Pa. Further, thesubstrate 1 to be processed, which is housed in the chamber 11, isheated to 300° C. by the heating means arranged in, for example, thelower electrode 13. Then, the high frequency power source apparatus 14is operated so as to supply a high frequency power of output voltage 500W and frequency 40 MHz between the electrodes 12 and 13 through thematching device 15. As a result, a plasma is generated within thechamber 11. Since the free space within the chamber 11 is rich in the Xegas as a rare gas, a high electron density is maintained within thechamber 11. It follows that a plasma is generated at a high density soas to permit the O₂ gas used as the oxidizing gas and the TEOS gas usedas the silicon compound gas to be decomposed efficiently by the plasma.As a result, silicon oxide molecules (SiO₂) are deposited on one surfaceof the substrate 1 to be processed so as to form a silicon oxide film(SiO₂ film).

The characteristics of the SiO₂ film formed by the film-forming methodaccording to the first embodiment of the present invention wereevaluated as follows.

Specifically, prepared were a plurality of different kinds of mixedgases differing from each other in the percentage of the partialpressure of the Xe gas based on the total pressure of the mixed gas,followed by forming a SiO₂ film by the method described above in respectof each kind of the mixed gas. Then, an aluminum electrode was formed bymeans of a vapor deposition on the SiO₂ film thus formed so as to obtaina metal oxide semiconductor device (i.e., MOS device). The flat bandvoltage of each of the MOS devices was determined by measuring thecapacitance-voltage characteristics of the SiO₂ film included in each ofthe MOS devices.

FIG. 2 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas (Pr) contained in the mixed gas and theflat band voltage of the MOS device. Incidentally, since a large numberof stationary charges are contained in general in the SiO₂ film, theflat band voltage is shifted in the negative direction.

As shown in FIG. 2, the flat band voltage was held substantiallyconstant at about −2.3V in the conventional MOS device in which the SiO₂film was formed under the state that the percentage of the partialpressure of the Xe gas (Pr) contained in the mixed gas was set lowerthan 85%, i.e., 0%≦Pr<85%. On the other hand, the flat band voltage wasfound to fall within a range of between about −2.0V and about −1.0V inthe MOS device according to the first embodiment of the presentinvention in which the SiO₂ film was formed under the state that thepercentage of the partial pressure of the Xe gas (Pr) contained in themixed gas was set at a level not smaller than 85%, i.e., 85%≦Pr<100%. Inother words, the absolute value of the flat band voltage for the MOSdevice according to the first embodiment of the present invention wasfound to be smaller than that for the conventional MOS device.

It was necessary in the past for the stationary charge density of theSiO₂ film to be low. The small absolute value of the flat band voltageimplies that the stationary charge density of the film is lowered. Inother words, it has been found that it is possible to obtain a SiO₂having a low stationary charges density by forming the SiO₂ under thestate that the percentage of the partial pressure of the Xe gas (Pr)contained in the mixed gas is set at a level not smaller than 85%, i.e.,85%≦Pr<100%, as in the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas (Pr) contained in the mixed gas and theelectron density in the mixed gas.

As shown in FIG. 3, the electron density in the mixed gas is about 10⁹cm⁻³ under the state that the percentage of the partial pressure of theXe gas (Pr) contained in the mixed gas is lower than 85%, i.e.,0%≦Pr<85%. However, the electron density in the mixed gas is increasedto about 10¹⁰ to 10¹² cm⁻³, which is tens to hundreds of times as highas that in the case referred to above, if the percentage of the partialpressure of the Xe gas in the mixed gas (Pr) is set at a level notsmaller than 85%, i.e., 85%≦Pr<100%, as defined in the presentinvention.

The experimental data support that the electron density in the plasmawas rapidly increased in the film-forming method according to the firstembodiment of the present invention. It is considered reasonable tounderstand that, since the Xe gas is formed of monatomic molecules, theelectrons in the plasma are free from the energy loss in thefilm-forming method according to the first embodiment of the presentinvention, though the electrons in the plasma are caused to lose theenergy by the dissociating reaction in the case of using polyatomicmolecules. In other words, it is considered reasonable to understandthat, if the electrons are not caused to lose the energy by thedissociating reaction, the electron density in the plasma is increasedin the case where the supplied high frequency power is constant.

It follows that, according to the first embodiment of the presentinvention, it is possible to increase the electron density in the plasmaso as to promote the decomposition of the TEOS gas and the O₂ gasachieved by the plasma. As a result, it is possible to form efficientlythe Si atoms and the O atoms. It should also be noted that, if the Oatoms are formed efficiently, it is possible to suppress the oxygendeficiency in the SiO₂ film, with the result that the current leakagethrough the SiO₂ film formed can be diminished.

Second Embodiment

In the first embodiment described above, the gaseous pressure within thechamber 11 is set at 60 Pa. As a result, the percentage of the partialpressure of the TEOS gas based on the total pressure of the mixed gas isdecreased with increase in the percentage of the partial pressure of therare gas (Xe gas) based on the total pressure of the mixed gas, i.e.,with increase in the degree of dilution with the rare gas. It followsthat it is possible for the film-forming rate to be lowered depending onthe percentage of the partial pressure of the rare gas (Pr) based on thetotal pressure of the mixed gas. Since the manufacturing time is one ofthe factors determining the manufacturing cost of the product, it isdesirable for the film-forming time to be short. Such being thesituation, a second embodiment of the present invention is directed to afilm-forming method that permits improving the film-forming rate.

In the first step, a mixed gas is formed of gases including a siliconcompound gas consisting of compounds having silicon atoms, an oxidizinggas and a rare gas. In the second embodiment of the present invention,prepared are a TEOS gas acting both as a silicon compound gas and as anorganometallic compound gas, an O₂ gas acting as an oxidizing gas, and aXe gas used as a rare gas.

In the next step, the TEOS gas and the O₂ gas, which are mixed at amixing ratio of 1:5, are supplied into the chamber 11 such that the sumof the partial pressures of these gases is 10 Pa, followed by supplyinga Xe gas into the chamber 11 such that the percentage (diluting rate) ofthe partial pressure of the Xe gas (Pr) based on the total pressurewithin the chamber 11 is not smaller than 85%, i.e., 85%≦Pr<100%. As aresult, a mixed gas is formed within the chamber 11. The other steps areequal to those for the first embodiment and, thus, the description ofthe overlapping portion is omitted.

FIG. 4 is a graph showing the relationship between the percentage of thepartial pressure of the Xe gas (Pr) contained in the mixed gas and theforming rate of a SiO₂ film.

As shown in FIG. 4, the film-forming rate was maintained substantiallyconstant at about 20 nm/min under the state that the percentage of thepartial pressure of the Xe gas (Pr) contained in the mixed gas was lowerthan 90%, i.e., 0%≦Pr<90%. On the other hand, the film-forming rate wasincreased from about 20 nm/min to about 55 nm/min in the case where thepercentage of the partial pressure of the Xe gas (Pr) contained in themixed gas was set to fall within a range of between 90% and 98%, i.e.,90%≦Pr<98%.

A SiO₂ film was also formed under the conditions that the percentage ofthe partial pressure of the Xe gas (Pr) contained in the mixed gas wasset at 95% and that the total pressure of the mixed gas was set at 200Pa. Then, an aluminum electrode was formed by means of a vapordeposition on the SiO₂ film so as to obtain a MOS device. When the flatband voltage of the MOS device was measured, it was found that theabsolute value of the flat band voltage was lowered, compared with theconventional MOS device. It follows that the film-forming rate isincreased and the effect of improving the quality of the film can beobtained, if the SiO₂ film is formed under the conditions that thepercentage of the partial pressure of the Xe gas (Pr) contained in themixed gas is set at 95% and that the total pressure of the mixed gas isset at 200 Pa.

The density of the stationary charge is low as long as the TEOS gas andthe O₂ gas are contained in the mixed gas even if the amounts of thesegases are very small. In addition, it is possible to form a SiO₂ filmthat has a low current leakage. However, the film-forming rate islowered, if the mixed gas is diluted by the Xe gas such that thepercentage of the partial pressure of the Xe gas (Pr) based on the totalpressure of the mixed gas is increased to exceed 98%. It follows that,in order to increase the film-forming rate and to obtain a satisfactoryeffect of improving the film quality, it is desirable for the percentageof the partial pressure of the Xe gas (Pr) based on the total pressureof the mixed gas to fall within a range of between 90% and 98%, i.e.,90%≦Pr<98%.

As described above, the film-forming method according to the first andsecond embodiments of the present invention comprises the steps ofsupplying into a plasma processing chamber (chamber 11) at least threekinds of gases including a silicon compound gas formed of a compoundhaving a silicon atom (i.e., a TEOS gas in each of the first and secondembodiments, which is also an organometallic compound gas), an oxidizinggas, and a rare gas, the percentage of the partial pressure of the raregas (Pr) based on the total pressure of all the gases being not smallerthan 85%, i.e., 85%≦Pr<100%; and generating a plasma within the plasmaprocessing chamber so as to permit the silicon compound gas and theoxidizing gas to be decomposed by the plasma, thereby forming a filmconsisting of silicon oxide on a substrate to be processed. It followsthat, in the film-forming method according to the first and secondembodiments of the present invention, it is possible to form a SiO₂ filmthat is low in the oxygen deficiency easily at a low cost.

Also, in the film-forming method according to the first and secondembodiments of the present invention, it is possible to obtain a SiO₂film, which is low in the density of the stationary charge and in thecurrent leakage. In other words, the characteristics of the SiO₂ filmcan be improved. In addition, it is possible to form the SiO₂ at about300° C., which is lower than the temperature employed in theorganometallic gaseous phase growth method.

Further, the film-forming rate can be rendered higher than that in theconventional method by allowing the percentage of the partial pressureof the rare gas (Pr) based on the total pressure to fall within a rangeof between 90% and 98%, i.e., 90%≦Pr<98%.

Incidentally, in each of the first and second embodiments of the presentinvention described above, a Xe gas was used as the rare gas. However,it is also possible to use a krypton (Kr) gas, an argon (Ar) gas, a neon(Ne) gas or a helium (He) gas as the rare gas. It should be noted,however, that the silicon compound gas (organometallic compound gas) andthe oxidizing gas can be decomposed efficiently by the plasma, if theelectron density is high. It follows that it is desirable for the raregas to exhibit a high electron density. Under the circumstances, theorder of preference of the rare gas to be used is Xe gas>Kr gas>Argas>Ne gas>He gas in order to increase the electron density within theplasma processing chamber (chamber 11).

Third Embodiment

In the first step, prepared is the substrate 1 to be processed. It ispossible to use, for example, a silicon substrate for forming asemiconductor device, a glass substrate for forming the display circuitfor a liquid crystal display device or a plastic substrate as thesubstrate 1 to be processed as in the first embodiment describedpreviously. A silicon substrate is used in the third embodimentdescribed in the following.

In the next step, prepared is a mixed gas consisting of at least threekinds of gases including a silicon compound gas, an oxidizing gas and ahydrogen gas (H₂ gas). It is also possible to mix the silicon compoundgas, the oxidizing gas and the hydrogen gas when these gases areintroduced into the chamber 11 so as to form a desired mixed gas.

In the third embodiment of the present invention, the mixed gas isprepared by mixing a TEOS gas, which is used as a silicon compound gasand as an organometallic compound gas, an O₂ gas used as an oxidizinggas, and a H₂ gas. The mixing ratio of the TEOS gas to the O₂ gas in themixed gas is 1:15. Also, the percentage of the partial pressure of theH₂ gas (Ph) based on the total pressure of the mixed gas, which is 100%,is set at a level not larger than 3%, i.e., 0%<Ph≦3%.

In the third embodiment of the present invention, prepared were twokinds of the mixed gases consisting of a mixed gas in which the mixingratio of the TEOS gas to the O₂ gas was set at 1:15 and the percentageof the partial pressure of the H₂ gas (Ph) contained in the mixed gaswas set at 0.5%, and another mixed gas in which the mixing ratio of theTEOS gas to the O₂ gas was set at 1:15 and the percentage of the partialpressure of the H₂ gas (Ph) contained in the mixed gas was set at 3%.

In the next step, the substrate 1 to be processed was housed in thechamber 11 of the plasma CVD apparatus 10 shown in FIG. 1. The plasmaCVD apparatus used was equal to that used in the first embodimentdescribed previously and, thus, the overlapping description is omitted.

Then, the vacuum exhaust system was operated so as to set up asubstantially vacuum condition substantially reaching a desired degreeof vacuum within the chamber 11. After the chamber 11 was evacuated soas to set up a vacuum condition, the mixed gas was supplied into thechamber 11 until the gaseous pressure within the chamber 11 wasincreased to reach 80 Pa. Then, the substrate 1 to be processed washeated to, for example, 300° C. by the heating means arranged within thelower electrode 13. Further, the high frequency power source apparatus14 was operated so as to supply a high frequency power between theelectrodes 12 and 13 through the matching device 15, thereby generatinga plasma within the chamber 11. The TEOS gas is decomposed within theplasma so as to form Si atoms. Also, a reaction is carried out betweenthe H₂ gas and the O₂ gas so as to form O atoms efficiently. As aresult, SiO₂ molecules are deposited on the substrate 1 to be processedso as to form a SiO₂ film.

The characteristics of the SiO₂ film formed by the film-forming methodaccording to the third embodiment of the present invention wereevaluated as follows.

In the first step, mixing gas conditions 1) to 3) given below wereprepared:

1) The mixing gas condition under which the TEOS gas was mixed with theO₂ gas at a mixing ratio of 1:15 as in the conventional method.

2) The mixing gas condition under which the TEOS gas was mixed with theO₂ gas at a mixing ratio of 1:15, and the percentage of the partialpressure of the H₂ gas (Ph) contained in the mixed gas was set at 0.5%,as in the third embodiment of the present invention.

3) The mixing gas condition under which the TEOS gas was mixed with theO₂ gas at a mixing ratio of 1:15, and the percentage of the partialpressure of the H₂ gas (Ph) contained in the mixed gas was set at 3%, asin the third embodiment of the present invention.

A SiO₂ film was formed as described above under each of conditions 1) to3) given above, followed by forming by means of a vapor deposition analuminum electrode on the SiO₂ film thus formed so as to obtain a MOSdevice. Then, the flat band voltage of each of the MOS devices wasdetermined by measuring the capacitance-voltage characteristics of theSiO₂ film included in each of the MOS devices.

FIG. 5 is a graph showing the relationship between the percentage of thepartial pressure of the H₂ gas (Ph) contained in the mixed gas and theflat band voltage of the MOS device.

As shown in FIG. 5, the flat band voltage was about −2.0V in theconventional MOS device in which the SiO₂ film was formed under themixing gas condition 1) given above. On the other hand, the flat bandvoltage was found to be about −1.8V in the MOS device in which the SiO₂film was formed under the mixing gas condition 2) given above. Further,the flat band voltage was found to be about −1.4V in the MOS device inwhich the SiO₂ film was formed under the mixing gas condition 3) givenabove. In other words, the absolute value of the flat band voltage wasfound to be smaller in the MOS device according to the third embodimentof the present invention than that in the conventional MOS device. Inother words, it has been found that a SiO₂ film having a low stationarycharge density can be formed by adding H₂ gas to the mixed gas.

It is considered reasonable to understand that, since the H₂ gas iscapable of reacting with the O₂ gas, the oxygen atoms can be formedefficiently so as to form a SiO₂ film having a low stationary chargedensity. What should be noted is that, in the film-forming methodaccording to the third embodiment of the present invention, the oxygenatoms can be formed efficiently so as to suppress the oxygen deficiencyin the SiO₂ film, with the result that it is possible to suppress thecurrent leakage through the SiO₂ film.

Incidentally, the O₂ gas and the H₂ gas are present together in themixed gas. Therefore, if the percentage of the partial pressure of theH₂ gas (Ph) contained in the mixed gas is increased to reach 4% or more,it is possible for the H₂ gas to react with the O₂ gas explosively. Itfollows that, if the percentage of the partial pressure of the H₂ gas(Ph) is set at 4% or more, careful attention is required in thefilm-forming process and in the film-forming apparatus. Naturally, it isnot desirable to set the percentage of the partial pressure of the H₂gas (Ph) at 4% or more. The effect described above can be obtained ifthe H₂ gas is contained in the mixed gas. It follows that, in view ofthe safety and the manufacturing cost, it is desirable to set thepercentage (diluting rate) of the partial pressure of the H₂ gas (Ph)contained in the mixed gas at a level smaller than 3%, i.e., 0%≦Ph<3%.

As described above, the film-forming method according to the thirdembodiment of the present invention comprises the steps of supplyinginto a plasma processing chamber (chamber 11) at least three kinds ofgases including a silicon compound gas formed of a compound havingsilicon atoms (i.e., a TEOS gas, which also constitutes anorganometallic compound gas, being used in the third embodiment), anoxidizing gas, and a hydrogen gas; and generating a plasma within theplasma processing chamber so as to permit the silicon compound gas, theoxidizing gas and the H₂ gas to be decomposed by the plasma, therebyforming a SiO₂ film on a substrate to be processed. It follows that thefilm-forming method according to the third embodiment of the presentinvention makes it possible to form a SiO₂ film, which is small in theoxygen deficiency, easily, and at a low cost.

Also, in the film-forming method according to each of the first andsecond embodiments of the present invention, it is possible to obtain aSiO₂ film, which is low in the stationary charge density and small inthe current leakage. In other words, it is possible to improve thecharacteristics of the SiO₂ film. In addition, the SiO₂ film can beformed at about 300° C., which is lower than that in the organometallicgaseous phase growth method.

Incidentally, a TEOS gas, which is also an organometallic compound gas,is used as a gas of a silicon compound having a Si atom. However, it isalso possible to use as the silicon compound gas a gas of any oftetramethyl cyclo-tetrasiloxane, di-acetoxy di-tertiary butoxy silane,and hexamethyl disiloxane. It is also possible to use as the siliconcompound gas any of a SiH₄ gas, a Si₂H₆ gas, a SiF₄ gas, a SiCl₄ gas, aSiH₂Cl₂ gas, and a mixed gas containing gases of at least two of theseSi-containing compounds.

Also, in each of the first to third embodiments of the present inventiondescribed above, an O₂ gas was used as an oxidizing gas. However, it isalso possible to use as the oxidizing gas at least one of an O₃ (ozone)gas, N₂O (dinitrogen oxide) gas, a NO (nitrogen monoxide) gas, a CO(carbon monoxide) gas, and a CO₂ (carbon dioxide) gas. Among theseoxidizing gases, it is desirable to use an O₃ gas because the O₃ gas canbe decomposed easily and has a high reactivity, compared with the otheroxidizing gas. The silicon compound gas is preferably SiH₄ gas, and theoxidizing gas is preferably at least one of O₃ gas and O₂ gas.

It should be noted that, if a gas of a compound having a nitrogen (N)atom such as a N₂O gas or a NO gas is used as the oxidizing gas, thenitrogen atoms are localized at the interface. Therefore, the interfacestate density is increased in the case of depositing SiO₂ molecules,which is not desirable for the semiconductor device. The particulartendency is rendered prominent with increase in the electron density inthe plasma. In other words, the particular tendency is renderedprominent in the film-forming method described in conjunction with thefirst to third embodiments of the present invention.

On the other hand, it is desirable to use as the oxidizing gas a gas ofthe compound having a carbon atom such as a CO gas or a CO₂ gas. It isconsidered reasonable to understand that, since the TEOS gas itself hascarbon atoms, the impurity of the SiO₂ film formed is not affected evenif a gas having carbon atoms such as a CO gas or a CO₂ gas is used asthe oxidizing gas.

Also, in the case of using a TEOS gas as a gas of a compound having a Siatom, it is possible to form a SiO₂ film that is satisfactory in itscoverage properties. Therefore, it is desirable to use the TEOS gas inthe case where it is necessary to form a SiO₂ film in a selected regionhaving an irregularity on the surface like the thin film transistor(TFT) included in a liquid crystal display device 20 shown in FIG. 10.In other words, a TFT including a gate insulating film satisfactory inits insulating properties can be obtained by forming a gate insulatingfilm of a SiO₂ film by using a TEOS gas as a silicon compound gas of acompound having a Si atom.

Such being the situation, it is desirable to use a TEOS gas as a siliconcompound gas in order to form a SiO₂ that is satisfactory in itscoverage properties. Also, in the case where a TEOS gas is used as asilicon compound gas, it is desirable to use at least one kind of gasselected from the group consisting of an O₂ gas, an O₃ gas, a CO gas,and a CO₂ gas as an oxidizing gas.

On the other hand, in the case where a gas of an inorganic compound suchas a SiH₄ gas or a Si₂H₆ gas is used as the silicon compound gas, it ispossible for the carbon atoms contained in the CO gas or the CO₂ gasused as an oxidizing gas to constitute impurities in the process offorming a SiO₂ film. Therefore, in the case of using a silane gas as asilicon compound gas, it is desirable to use as the oxidizing gas atleast one kind of the gas selected from the group consisting of the O₂gas and the O₃ gas. In this case, it is possible to form a SiO₂ filmhaving a high purity.

It should be noted that the effect produced by the first to thirdembodiments of the present invention is not affected by the excitingfrequency of the plasma and by the plasma source.

In order to obtain a plasma having a higher density, it is desirable touse a microwave having a high exciting frequency, e.g., a frequency of2.45 GHz or higher. It is advisable to use, for example, a surface waveplasma, which is one of microwave plasma sources free from a magneticfield, as the plasma source using a microwave.

Fourth Embodiment

A microwave plasma CVD apparatus 50 free from a magnetic field, which isused in a fourth embodiment of the present invention, will now bedescribed with reference to FIG. 6.

The microwave plasma CVD apparatus 50 free from a magnetic fieldcomprises a vacuum chamber 51 acting as a plasma processing vessel, amicrowave source 52, a waveguide 53, a plurality of slots 54, adielectric member 55, a gas inlet port 56, a gas evacuation port 57 anda substrate table 58.

The substrate table 58 is arranged within the vacuum chamber 51. A gate(not shown) is arranged in the vacuum chamber 51. The gate performs thefunction of transferring the substrate 1 to be processed, e.g., a glasssubstrate on which is formed a display circuit of a liquid crystaldisplay device such as a transistor, into and out of the vacuum chamber51. The vacuum chamber 51 has an effective processing area of, forexample, 70 cm×60 cm. The microwave source 52 generates a microwavehaving a frequency of, for example, 2.45 GHz. The waveguide 53, which isformed of, for example, a rectangular waveguide, has a width of, forexample, 9 cm and a height of, for example, 3 cm.

A plurality of slots 54 are formed in a side wall 53 a of the waveguide53, the side wall being positioned to face the upper wall of the vacuumchamber 51. The dielectric member 55 provides a window having athickness large enough to withstand the vacuum condition formed withinthe vacuum chamber 51 and formed of a material that permits transmittingthe microwave. For example, the dielectric member 55 is formed ofquartz, glass or a ceramic material. The gas inlet 56 is connected to avessel housing a raw material gas by a pipe such that the raw materialgas is supplied into the vacuum chamber 51 at a prescribed flow rate anda prescribed flowing speed. Further, the gas evacuation port 57 isformed of a pipe for releasing the gas after the processing from withinthe vacuum chamber 51 to the outside.

The vacuum chamber 51 is evacuated first to a prescribed degree ofvacuum. Then, a mixed gas containing the raw material gas is suppliedthrough the gas inlet 56 into the vacuum chamber 51 at a prescribed flowrate and a prescribed flowing speed. The microwave oscillated from theoscillator included in the microwave source 52 is propagated through thewaveguide 53 so as to be radiated into the vacuum chamber 51 through theslots 54 forming a waveguide antenna and the dielectric body member 55.In the apparatus 50 shown in FIG. 6, a plasma is generated by themicrowave radiated from the slots 54 into the vacuum chamber 51 so as tocarry out the film-forming operation.

The film-forming method according to a fourth embodiment of the presentinvention will now be described with reference to the plasma CVDapparatus 50 shown in FIG. 6.

In the first step, the substrate 1 to be processed is prepared. It ispossible to use as the substrate 1 to be processed any of a siliconsubstrate for forming a semiconductor device such as a transistor, aglass substrate for forming a display circuit of a liquid crystaldisplay device, and a plastic substrate. In the fourth embodiment of thepresent invention, a silicon substrate is used as the substrate 1 to beprocessed.

In the next step, a mixed gas including an organometallic compound gas,an oxidizing gas and a rare gas is prepared. Incidentally, it is alsopossible to mix the organometallic compound gas, the oxidizing gas andthe rare gas in the process of introducing these gases into the vacuumchamber 51 so as to prepare a desired mixed gas.

In the fourth embodiment of the present invention, a tripropoxy hafnium(Hf(OC₃H₇)₃) gas used as an organometallic compound gas, an O₂ gas usedas an oxidizing gas, and an Ar gas used as a rare gas are mixed so as toprepare the mixed gas. The percentage (diluting rate) of the partialpressure of the Ar gas (Pr) contained in the mixed gas is not smallerthan 85%, i.e., 85%≦Pr<100%. For example, the percentage Pr noted aboveis set at 90%. To be more specific, the mixing ratio of the tripropoxyhafnium gas: the O₂ gas: the Ar gas is set at 2%:8%:90% in the fourthembodiment of the present invention.

In the next step, the substrate 1 to be processed is housed in thevacuum chamber 51 of the plasma CVD apparatus 50, followed by operatingthe vacuum exhaust system so as to evacuate the vacuum chamber 51 in amanner to set up a condition substantially equal to the vacuum conditionwithin the vacuum chamber 51. Further, after the vacuum exhausttreatment is applied to the vacuum chamber 51, the mixed gas is suppliedinto the vacuum chamber 51 until the gaseous pressure within the vacuumchamber 51 is increased to reach 80 Pa. Then, a high frequency powersource apparatus (not shown) is operated so as to generate a surfacewave plasma, which is one of the microwave plasma sources free from amagnetic field, within the vacuum chamber 51 by use of a microwavehaving an output voltage of 1000 W and a frequency of 2.45 G. Since thefree space within the vacuum chamber 51 is rich in the Ar gas, a highelectron density is maintained within the vacuum chamber 51, with theresult that a surface wave plasma is generated at a high density. Itfollows that the O₂ gas and the tripropoxy hafnium gas can be decomposedefficiently by the plasma. As a result, the hafnium oxide (HfO₂)molecules are deposited on one surface of the substrate 1 to beprocessed so as to form a hafnium oxide film (HfO₂ film) having a highdielectric constant.

FIG. 7 is a graph showing the relationship between the percentage of thepartial pressure of the Ar gas (Pr) contained in the mixed gas and theelectron density.

As shown in FIG. 7, the electron density within the mixed gas is about10⁹ cm⁻³ in the case where the percentage of the partial pressure of theAr gas (Pr) contained in the mixed gas is smaller than 85%, i.e.,0%≦Pr<85%. On the other hand, where the percentage of the partialpressure of the Ar gas (Pr) contained in the mixed gas is not smallerthan 85%, i.e., 85%≦Pr<100%, the electron density within the mixed gasis about 10¹⁰ to 10¹² cm⁻³, which is tens to hundreds of times as highas that in the case where the percentage Pr noted above is smaller than85%.

The experimental data given above support that it is possible toincrease rapidly the electron density within the plasma in thefilm-forming method according to the fourth embodiment of the presentinvention. It is considered reasonable to understand that, since the Argas is formed of monatomic molecules like the Xe gas, the electrons inthe plasma are free from the energy loss in the film-forming methodaccording to the fourth embodiment of the present invention, though theelectrons in the plasma are caused to lose their energy by thedissociating reaction in the case of using polyatomic molecules. Inother words, it is considered reasonable to understand that, if theelectrons are not caused to lose their energy by the dissociatingreaction, the electron density in the plasma is increased in the casewhere the supplied high frequency power is constant.

Fifth Embodiment

The CVD apparatus shown in FIG. 1 is used in a fifth embodiment of thepresent invention. In the first step, the substrate 1 to be processed isprepared. It is possible to use, for example, a silicon substrate, aglass substrate or a plastic substrate as the substrate 1 to beprocessed. In the fifth embodiment, the substrate 1 to be processed isformed of, for example, silicon.

In the next step, a mixed gas including an organometallic compound gas,an oxidizing gas and a H₂ gas is prepared. In the fifth embodiment ofthe present invention, the mixed gas is prepared by mixing a tripropoxyhafnium gas used as an organometallic compound gas, an O₂ gas used as anoxidizing gas, and a H₂ gas. It is desirable for the percentage(diluting rate) of the partial pressure of the H₂ gas (Ph) contained inthe mixed gas to be set at a level smaller than 3%, i.e., 0%≦Ph<3%. Ifthe percentage of the partial pressure of the H₂ gas (Ph) contained inthe mixed gas is increased to reach 4% or more, it is possible for theH₂ gas to react with the O₂ gas explosively, as already described inconjunction with the third embodiment of the present invention. To bemore specific, the mixing ratio of the tripropoxy hafnium gas: the O₂gas: H₂ gas is set at 20%:78%:2% in the fifth embodiment of the presentinvention.

In the next step, the substrate 1 to be processed is housed in thevacuum chamber 11 included in the plasma CVD apparatus 10, followed byoperating the vacuum exhaust system so as to establish a conditionsubstantially equal to the vacuum condition within the vacuum chamber11. Further, after the vacuum chamber 11 is evacuated so as to set up avacuum condition, the mixed gas is supplied into the vacuum chamber 11until the gaseous pressure within the vacuum chamber 11 is increased toreach 80 Pa. Then, the high frequency power source apparatus 14 isoperated so as to generate a surface wave plasma, which is one ofmicrowave plasma sources free from a magnetic field, within the vacuumchamber 11 by using a microwave of 1,000 W and 2.45 G. Within thesurface wave plasma, the tripropoxy hafnium gas is decomposed so as togenerate Hf atoms. Also, the reaction is carried out between the H₂ gasand the O₂ gas within the surface wave plasma so as to form O atomsefficiently. As a result, HfO₂ molecules are deposited on the substrate1 to be processed so as to form a HfO₂ film having a high dielectricconstant.

The characteristics of the HfO₂ film formed by the film-forming methodaccording to each of the fourth and fifth embodiments of the presentinvention were evaluated as follows.

Specifically, a HfO₂ film was formed on a silicon substrate by each ofthe conventional film-forming method, in which was used a mixed gasprepared by mixing a tripropoxy hafnium gas and an O₂ gas at a mixingratio of 20%:80%, the film-forming method according to the fourthembodiment of the present invention and the film-forming methodaccording to the fifth embodiment of the present invention. Then, thecurrent-voltage characteristics were measured for each of these HfO₂films.

FIG. 8 is a graph showing the current leakage at the time when anelectric field of 2MV/cm was applied to each of the HfO₂ film formed bythe conventional film-forming method, the HfO₂ film formed by thefilm-forming method according to the fourth embodiment of the presentinvention, and the HfO₂ film formed by the film-forming method accordingto the fifth embodiment of the present invention.

As shown in FIG. 8, the current leakage was about 10⁻¹¹ (A) in the caseof the HfO₂ film formed by the conventional film-forming method. On theother hand, the current leakage was about 10⁻¹² (A) in the case of theHfO₂ film formed by the film-forming method according to the fourth andfifth embodiments of the present invention. It follows that thefilm-forming method according to the fourth and fifth embodiments of thepresent invention permits lowering the current leakage through the metaloxide film, compared with the conventional film-forming method.

It is considered reasonable to understand that the particular effect ofthe present invention is produced as follows. Specifically, in thefilm-forming method according to the fourth embodiment of the presentinvention, the plasma density is increased so as to permit thetripropoxy hafnium gas and the O₂ gas to be decomposed efficiently bythe plasma. As a result, the HfO₂ film formed is densified so as todecrease the amount of the oxygen deficiency.

Also, in the film-forming method according to the fifth embodiment ofthe present invention, the reaction is carried out between the O₂ gasand the H₂ gas within the plasma so as to generate O atoms and H atoms.As a result, the amount of the oxygen deficiency in the resultant HfO₂film is considered to be decreased so as to cause the oxygen defect tobe terminated with hydrogen.

Also, in the film-forming method according to the fourth embodiment ofthe present invention, the mixed gas used is prepared by mixing anorganometallic compound gas, an oxidizing gas and a rare gas such thatthe percentage of the partial pressure of the rare gas (Pr) based on thetotal pressure of the mixed gas is set at a level not smaller than 85%,i.e., 85%≦Pr<100%. As a result, the carbon atom concentration in thefilm can be suppressed in the fourth embodiment as in a sixth embodimentof the present invention that is to be described herein later.

Further, in the film-forming method according to the fifth embodiment ofthe present invention, a film is formed by using a mixed gas prepared bymixing an organometallic compound gas, an oxidizing gas and a hydrogengas. As a result, the carbon atom concentration in the film can besuppressed in the fifth embodiment as in a seventh embodiment of thepresent invention that is to be described herein later.

According to each of the fourth and fifth embodiments of the presentinvention, it is possible to form a metal oxide film, which is small inoxygen deficiency, easily, and at a low cost. It is also possible todecrease the current leakage through the metal oxide film and tosuppress the carbon atom concentration in the film so as to improve thecharacteristics of the film.

Sixth Embodiment

In a sixth embodiment of the present invention, a mixed gas is preparedby mixing a trimethyl aluminum gas (TMA gas) used as an organometalliccompound gas, an O₂ gas used as an oxidizing gas and a Kr gas used as arare gas. Also, the percentage (diluting rate) of the partial pressureof the Kr gas (Pr) contained in the mixed gas is set at a level notsmaller than 85%, i.e., 85%≦Pr<100%. For example, the percentage Prnoted above is set at 98%. To be more specific, the mixing ratio of theTMA gas, the O₂ gas and the Kr gas is set at 0.5%:1.5%:98%.Incidentally, the sixth embodiment is equal to the fourth embodiment inthe other steps and, thus, the overlapping description is omitted. Inthis fashion, an Al₂O₃ film is formed in the sixth embodiment of thepresent invention.

Seventh Embodiment

In a seventh embodiment of the present invention, a mixed gas isprepared by mixing a TMA gas used as an organometallic compound gas, anO₂ gas used as an oxidizing gas and a H₂ gas. To be more specific, themixing ratio of the TMA gas, the O₂ gas and the H₂ gas is set at10%:89%:1%. Incidentally, the seventh embodiment is equal to the fifthembodiment in the other steps and, thus, the overlapping description isomitted. In this fashion, an Al₂O₃ film is formed in the seventhembodiment of the present invention.

The characteristics of the Al₂O₃ film formed by the film-forming methodaccording to each of the sixth and seventh embodiments of the presentinvention were evaluated as follows.

Specifically, an Al₂O₃ film was formed in a thickness of 200 nm on asilicon substrate by each of the conventional film-forming method, inwhich was used a mixed gas prepared by mixing a TMA gas and an O₂ gas ata mixing ratio of 10%:90%, the film-forming method according to thesixth embodiment of the present invention and the film-forming methodaccording to the seventh embodiment of the present invention. Then, thecarbon concentration in the Al₂O₃ film was measured by SIMS (secondaryion mass spectrometry) for each of the Al₂O₃ films. Incidentally, thepressure of the plasma was 80 Pa and the power was 1,000 W.

FIG. 9 is a graph showing the carbon atom concentration in each of theAl₂O₃ film formed by the conventional film-forming method, the Al₂O₃film formed by the film-forming method according to the sixth embodimentof the present invention, and the Al₂O₃ film formed by the film-formingmethod according to the seventh embodiment of the present invention.

As shown in FIG. 9, the carbon atom concentration was about 10²¹atoms/cm³ in the Al₂O₃ film formed by the conventional film-formingmethod. On the other hand, the carbon atom concentration was about 10¹⁹atoms/cm³ in the Al₂O₃ film formed by the film-forming method accordingto the sixth or seventh embodiment of the present invention. It followsthat the film-forming method according to the sixth embodiment and theseventh embodiment of the present invention makes it possible to lowerthe carbon atom concentration, compared with the conventionalfilm-forming method.

The low carbon atom concentration achieved by the film-forming methodaccording to the sixth embodiment of the present invention is derivedfrom the situation that the plasma density is increased by the rare gas(Kr gas) so as to improve the efficiency of forming the oxygen atoms. Inother words, if the number of oxygen atoms is increased, the amounts ofCO and CO₂ formed by the combustion reaction with carbon are increased.It is considered reasonable to understand that, since CO and CO₂, whichare high in volatility, tend to be discharged without being taken in thefilm, the carbon atom concentration in the film is lowered.

Also, in the film-forming method according to the seventh embodiment ofthe present invention, it is considered reasonable to understand that alarge number of oxygen atoms are generated by the reaction between O₂and H₂ that is carried out within the plasma so as to lower the carbonatom concentration in the film. If a large number of oxygen atoms aregenerated, the amounts of CO and CO₂ formed by the combustion reactionwith carbon are increased as in the sixth embodiment described above. Itis considered reasonable to understand that, since CO and CO₂, which arehigh in volatility, tend to be discharged without being taken in thefilm, the carbon atom concentration in the film is lowered.

Also, in the film-forming method according to the sixth embodiment ofthe present invention, a mixed gas is prepared by mixing anorganometallic compound gas, an oxidizing gas and a rare gas such thatthe percentage of the partial pressure of the rare gas (Pr) is set at alevel not smaller than 85%, i.e., 85%≦Pr<100%. It follows that,according to the film-forming method according to the sixth embodimentof the present invention, it is possible to decrease the current leakagethrough the metal oxide film as in the fourth embodiment of the presentinvention.

Further, in the film-forming method according to the seventh embodimentof the present invention, a mixed gas is prepared by mixing anorganometallic compound gas, an oxidizing gas and a hydrogen gas. Itfollows that, in the film-forming method according to the seventhembodiment of the present invention, it is possible to decrease thecurrent leakage through the metal oxide film as in the fifth embodimentof the present invention.

According to each of the sixth and seventh embodiments of the presentinvention, it is possible to form a metal oxide film, which is small inoxygen deficiency, easily, and at a low cost. Also, according to each ofthe sixth and seventh embodiments of the present invention, it ispossible to decrease the current leakage through the metal oxide filmand to suppress the carbon atom concentration in the film so as toimprove the characteristics of the film.

As described above, the film-forming method according to each of thefourth and sixth embodiments of the present invention comprises thesteps of supplying into a plasma processing chamber (chamber 11) atleast three kinds of gases including an organometallic compound gas, anoxidizing gas and a rare gas such that the percentage of the partialpressure of the rare gas (Pr) based on the total pressure is set at alevel not smaller than 85%, i.e., 85%≦Pr<100%; and generating a plasmawithin the plasma processing chamber so as to permit the organometalliccompound gas and the oxidizing gas to be decomposed by the plasma,thereby forming a metal oxide film on the substrate 1 to be processed.It follows that, in the film-forming method according to each of thefourth and sixth embodiments of the present invention, it is possible toform a metal oxide film, which has a high dielectric constant and is lowin oxygen deficiency, easily, and at a low cost.

Also, in the film-forming method according to each of the fourth andsixth embodiments of the present invention, it is possible to decreasethe current leakage through the metal oxide film and to suppress thecarbon atom concentration in the film so as to improve thecharacteristics of the metal oxide film. In addition, it is possible toform the metal oxide film at a temperature lower than that employed inthe organometallic gaseous phase growth method.

The film-forming method according to each of the fifth and seventhembodiments of the present invention comprises the step of supplyinginto a plasma processing chamber (chamber 11) at least three kinds ofgases including an organometallic compound gas, an oxidizing gas and ahydrogen gas, and the step of generating a plasma within the plasmaprocessing chamber so as to permit the organometallic compound gas, theoxidizing gas, and the hydrogen gas to be decomposed by the plasma,thereby forming a metal oxide film on the substrate 1 to be processed.It follows that, in the film-forming method according to each of thefifth and seventh embodiments of the present invention, it is possibleto form a metal oxide film, which has a high dielectric constant and islow in oxygen deficiency, easily, and at a low cost.

Also, in the film-forming method according to each of the fifth andseventh embodiments of the present invention, it is possible to decreasethe current leakage through the metal oxide film and to suppress thecarbon atom concentration in the film so as to improve thecharacteristics of the metal oxide film. In addition, it is possible toform the metal oxide film at a temperature lower than that employed inthe organometallic gaseous phase growth method.

Incidentally, in the film-forming method according to each of the fourthand fifth embodiments of the present invention, a tripropoxy hafnium gasis used as the organometallic compound gas. Also, in the film-formingmethod according to each of the sixth and seventh embodiments of thepresent invention, a TMA (Al(CH₃)₃) gas is used as the organometalliccompound gas. However, the organometallic compound used in the presentinvention is not limited to the gases exemplified above. Anorganometallic compound gas such as triethyl aluminum(Al(C₂H₅)₃) gas,tripropoxy zirconium(Zr(OC₃H₇)₃) gas, pentaethoxy tantalum(Ta(OC₂H5)₅)gas or the like can be used. It suffices to select an organometalliccompound gas containing the metal providing the raw material of themetal oxide film that is to be formed. To be more specific, it ispossible to form a HfO₂ film in the case of using a tripropoxy hafniumgas as the organometallic compound gas. Also, it is possible to form analuminum oxide (Al₂O₃) film in the case of using a trimethyl aluminumgas or a trimethyl aluminum gas as the organometallic compound gas.Further, it is possible to form a zirconium oxide (ZrO₂) film in thecase of using a tripropoxy zirconium gas as the organometallic compoundgas. Still further, it is possible to form a tantalum oxide (Ta₂O₅) filmin the case of using a pentaethoxy tantalum gas as the organometalliccompound gas.

Further, in each of the fourth to seventh embodiments of the presentinvention, a surface wave plasma is generated within the plasmaprocessing chamber (chamber 11), with the result that the organometalliccompound gas, etc. are decomposed by the plasma within the plasma of ahigh density, which is unlikely to do damage to the resultant metaloxide film.

Incidentally, in each of the first to seventh embodiments describedabove, a silicon substrate is used as the substrate 1 to be processed.However, it is also possible to use as the substrate 1 to be processedany of a silicon substrate, a glass substrate and a plastic substratehaving any of an insulating film, a metal film and a semiconductor filmformed thereon or a substrate having a laminate structure including aninsulating film, a metal film or a semiconductor film formed thereon.

A manufacturing method of a display device comprising a TFT will now bedescribed. Each of FIGS. 10 and 11 shows the construction of a displaydevice 20 such as an active matrix type liquid crystal display device.The display device 20 is called a liquid crystal display device in thefollowing description. Incidentally, a reference numeral 30 shown inFIG. 11 denotes a TFT.

The liquid crystal display device 20 will now be described first. Asshown in FIGS. 10 and 11, the liquid crystal display device 20 comprisesa pair of transparent substrates 21 and 22, a liquid crystal layer 23formed in a region surrounded by a sealing material between thetransparent substrates 21 and 22, a plurality of pixel electrodes 24arranged in the row direction and in the column direction on the innersurface of the transparent substrate 22 in a manner to form a matrix, atransparent counter electrode 27 in the form of a single film, which ispositioned to face the pixel electrodes 24, a plurality of TFTs 30arranged to form a matrix and each including a gate insulating film 36formed by the film-forming method that is to be described herein later,and a scanning line 25 and a signal line 26, which are electricallyconnected to these TFTs 30. In other words, the liquid crystal displaydevice 20 is constructed such that transistors, e.g., the TFTs 30, usedas the pixel selecting elements are arranged to form a matrix.

It is possible to use, for example, a pair of glass substrates as thepair of the transparent substrates 21 and 22. These transparentsubstrates 21 and 22 are bonded to each other with a frame-shapedsealing material (not shown) interposed therebetween. The liquid crystallayer 23 is arranged in a region surrounded by the sealing materialbetween the pair of the transparent substrates 21 and 22.

A plurality of pixel electrodes 24, a plurality of TFTs 30, the scanningline 25 and the signal line 26 are arranged on the inner surface of thetransparent substrate 22 on, for example, the back side. The pixelelectrodes 24 are arranged in the row direction and in the columndirection so as to form a matrix. The TFTs 30 are electricallyconnected, respectively, to the plural pixel electrodes 24. Further, thescanning line 25 and the signal line 26 are electrically connected toeach of the plural TFTs 30.

The scanning lines 25 are allowed to extend in the column direction ofthe pixel electrodes 24 and connected, respectively, at the ends on oneside to a plurality of scanning line terminals (not shown) formed in theedge portion on one side of the transparent substrate 22 on the backside. Also, the plural scanning line terminals are connected,respectively, to a scanning line driving circuit 41.

On the other hand, the signal lines 26 extend in the row direction ofthe pixel electrodes 24 and connected, respectively, at the ends on oneside to a plurality of signal line terminals (not shown) formed in theedge portion on one side of the transparent substrate 22 on the backside. Also, the plural scanning line terminals are connected,respectively, to a signal line driving circuit 42.

Each of the scanning line driving circuit 41 and the signal line drivingcircuit 42 is connected to a liquid crystal controller 43. Upon receiptof an image signal and a synchronizing signal supplied from, forexample, the outside, the liquid crystal controller 43 generates animage video signal V_(pix), a vertical scanning control signal YCR and ahorizontal scanning control signal XCT.

The transparent counter electrode 27 in the form of a single film, whichis positioned to face the plural pixel electrodes 24, is formed on theinner surface of another transparent substrate, i.e., the transparentsubstrate 21 on the front side. Also, it is possible to arrange a colorfilter on the inner surface of the transparent substrate 21 on the frontside in a manner to correspond to a plurality of pixel portions in whichthe plural pixel electrodes 24 are positioned to face the counterelectrode 27. Further, it is possible to form a light shielding film ina manner to correspond to the region between the pixel portions.

A polarizing plate (not shown) is formed on the outside of the pair ofthe transparent substrates 21 and 22. Also, in a transmission typeliquid crystal display device 20, a planar light source (not shown) isformed on the side of the back surface of the transparent substrate 22on the rear side. Incidentally, it is possible for the liquid crystaldisplay device 20 to be of a reflection type or of a semi-transmittingreflection type.

The construction of the TFT 30, i.e., a semiconductor device, will nowbe described. A reference numeral 31 shown in FIG. 11 denotes a bufferlayer consisting of SiO₂ and formed on the transparent substrate 22. Asemiconductor layer 32 comprising a source region 33, a drain region 34and a channel region 35 is formed on the buffer layer 31. A gateelectrode 37 consisting of Al is formed on the semiconductor layer 32with a gate insulating film 36 interposed therebetween. Further, aninterlayer insulating film 38 consisting of SiO₂ is formed on the entiresurface of the transparent substrate 22 including the gate electrode 37.

As shown in FIG. 11, the TFT 30 comprises the transparent substrate 22,the buffer layer 31 formed on the transparent substrate 22, thesemiconductor layer 32 including the source region 33, the drain region34 and the channel region 35, a gate insulating film 36 formed on thesemiconductor layer 32 by the film-forming method described herein laterand including a silicon oxide layer 36 a and an aluminum oxide layer 36b, and a gate electrode 37 formed on the gate insulating film 36.

The manufacturing method of the TFT 30 will now be described.Incidentally, in the manufacturing method described in the following, itis possible to form a plurality of TFTs 30 simultaneously on thetransparent substrate 22 on the rear side.

In the first step, a SiO₂ film acting as the buffer layer 31 is formedon substantially the entire region of the surface forming the innersurface of the transparent substrate 22 on the rear side. Then, anamorphous silicon (a-Si) film is formed on the buffer layer 31 in athickness of 100 nm by, for example, a reduced pressure CVD method,followed by applying a dehydrogenation treatment at 450° C. for one hourunder a nitrogen gas atmosphere. Further, the a-Si film is crystallizedby applying a laser annealing to the a-Si film by using an excimer laserso as to form a polycrystalline silicon layer.

In the next step, the polycrystalline silicon layer is coated by meansof a spin coating method with a resist film formed of a photosensitiveresin, followed by applying a light exposure and a development to theresist film by the photolithography process so as to form a plurality ofsemiconductor layers 32 each having a prescribed island shape. Each ofthese semiconductor layers 32 is formed to correspond to the TFT 30 soas to provide a constituting factor of the corresponding TFT 30. In thenext step, the gate insulating film 36 is formed to cover theisland-shaped semiconductor layer 32. The method of forming the gateinsulating film 36 will be described later.

After formation of the gate insulating film 36, a metal film, e.g., anAl film, which is to be processed into a plurality of gate electrodes37, is formed on the gate insulating film 36 by means of, for example, asputtering method, followed by applying a photo-lithography process andan etching process to the metal film so as to process the metal filminto the shape of a wiring, thereby forming a plurality of gateelectrodes 37. Each gate electrode 37 is formed above the semiconductorlayer 32 in a manner to correspond to a single semiconductor layer 32.In other words, each gate electrode 37 is formed to correspond to asingle TFT 30 like the semiconductor layer 32, thereby providing aconstituting factor of the corresponding TFT 30. Incidentally, it isalso possible to form the scanning line 25 in a manner to form anintegral structure together with the gate electrode 37.

In the next step, the semiconductor device 32 is doped selectively withan impurity such as phosphorus (P) by means of, for example, an ionimplantation. As a result, formed are a semiconductor layer having a lowresistivity, which is formed into the source region 33 and the drainregion 34, and the channel region 35 into which the impurity is notintroduced.

In the next step, a SiO₂ film is deposited on the entire surface of thetransparent substrate 22 by a plasma CVD method, followed by applying aheat treatment to the SiO₂ film at 600° C. so as to form the interlayerinsulating film 38. After formation of the interlayer insulating film38, contact holes 44 are formed in those portions of the interlayerinsulating film 38 which correspond to the source region 33, the drainregion 34 and the gate electrode 37 by the photolithography method andthe etching method. Further, a metal film that is formed into a sourceelectrode is formed so as to be connected to the source region 33. Alsoformed is another metal film that is to be formed into a drain electrodeso as to be connected to the drain region 34. As a result, a pluralityof TFTs 30 are formed. After formation of the TFT 30, the pixelelectrode 24 is formed so as to be connected to the source electrode. Atthe same time, formed is a signal electrode that is electricallyconnected to the drain electrode.

The gate insulating film 36 is formed by the film-forming methodaccording to the embodiment of the present invention describedpreviously. It follows that the film-forming method of the presentinvention is applied to a substrate 2 to be processed comprising thetransparent substrate 22 having the buffer layer 31 and theisland-shaped semiconductor layer 32 formed thereon.

The method of forming the gate insulating film 36 will now be described.In the first step, a SiO₂ film is formed in a thickness not smaller than2 nm, e.g., in a thickness of 2 nm, on substantially the entire regionof the substrate 2 to be process by the conventional film-formingmethod, i.e., a plasma CVD method using a mixed gas consisting of a TEOSgas and an O₂ gas, or a low temperature oxidizing method, i.e., a plasmaoxidation method or an optical oxidation method. Incidentally, the SiO₂film can be formed by employing the film-forming method according to anyof the first to third embodiments of the present invention. Then, anAl₂O₃ film is formed on substantially the entire surface of the SiO₂film by employing the film-forming method according to the sixthembodiment of the present invention. Incidentally, it is also possibleto form the Al₂O₃ film by employing the film-forming method according tothe seventh embodiment of the present invention. In other words, thegate insulating film 36 is of a laminate structure consisting of a SiO₂film 36 a and an Al₂O₃ film 36 b. It should be noted that the gateinsulating film 36, i.e., the laminate structure consisting of the SiO₂film 36 a and the Al₂O₃ film 36 b, has a dielectric constant larger thanthat of the conventional gate insulating film (SiO₂ film).

The characteristics of the gate insulating film 36 formed of thelaminate structure consisting of the SiO₂ film 36 a and the A₂o₃ film 36b were evaluated as follows. In the first step, MOS devices 1) to 3)given below were prepared:

1) A MOS device prepared by forming a SiO₂ film on a substrate by theplasma oxidation method, followed by forming an aluminum electrode onthe SiO₂ film by means of a vapor deposition.

2) A MOS device prepared by forming an Al₂O₃ film on a substrate by thefilm-forming method according to the sixth embodiment of the presentinvention, followed by forming an aluminum electrode on the Al₂O₃ filmby means of a vapor deposition.

3) A MOS device prepared by forming a SiO₂ film on a substrate by theconventional film-forming method, followed by forming an Al₂O₃ film onthe SiO₂ film by the film-forming method according to the sixthembodiment of the present invention and subsequently forming an aluminumelectrode on the Al₂O₃ film by means of a vapor deposition.

In the next step, the interface state density of each sample wasevaluated by measuring the capacitance-voltage characteristics of eachof the MOS devices thus prepared.

FIG. 12 is a graph showing the interface state density of each of theMOS devices.

As shown in FIG. 12, in the case where the Al₂O₃ film alone is formed onthe substrate, the interface state density is rendered higher than thatin the case where the SiO₂ film alone is formed on the substrate so asto lower the interface characteristics. However, it has been found thatthe interface state density is lowered in the case where the SiO₂ filmand the Al₂O₃ film are laminated one upon the other on the substrate soas to improve the interface characteristics. It is considered reasonableto understand that the interface state density is lowered in the casewhere the SiO₂ film is formed at the interface with the Al₂O₃ film.

It follows that, since the dielectric constant of the gate insulatingfilm 36 can be increased by forming the gate insulating film 36 asdescribed above, the effective thickness of the gate insulating film 36can be made smaller than that in the conventional device. Also, sincethe gate insulating capacitance can be increased by forming the gateinsulating film 36 as described above, it is possible to increase the ONcurrent of the TFT 30. Further, since the interface state density islow, it is possible to elevate the rising characteristics of the TFT 30.In addition, the gate insulating film 36 can be formed in thisembodiment at a temperature lower than that employed in theorganometallic gaseous phase growth method such that the damage done tothe underlayer can be lowered. Further, the gate insulating film 36 canbe formed at a film-forming rate higher than that for the atomic layerdepositing method.

As described above, the method of manufacturing a semiconductor deviceaccording to the present invention comprises the step of forming thesemiconductor layer 32 in at least a part on the surface of thesubstrate 2 to be processed, the step of laminating the silicon oxidelayer (SiO₂ layer) 36 a on the semiconductor layer 32, the step ofsupplying into a plasma processing chamber (chamber 11) at least threekinds of gases including an organometallic compound gas (TMA gas), anoxidizing gas, and a rare gas such that the percentage of the partialpressure of the rare gas (Pr) is not smaller than 85%, i.e.,85%≦Pr<100%, and the step of generating a plasma within the plasmaprocessing chamber so as to permit the organometallic compound gas andthe oxidizing gas to be decomposed by the plasma, thereby laminating analuminum oxide layer (Al₂O₃ film) 36 b as a metal oxide film on thesilicon oxide layer 36 a. It follows that, according to themanufacturing method of the semiconductor device outlined above, it ispossible to form an insulating film, which has a high dielectricconstant and is low in oxygen deficiency, easily, and at a low cost.Also, the manufacturing method of the semiconductor device defined inthe present invention makes it possible to decrease the thickness of theinsulating film. According to the manufacturing method of thesemi-conductor device, the electron density within the plasma processingchamber can be markedly higher than that in the conventional method,with the result that the decomposition of the organometallic compoundgas and the oxidizing gas is promoted.

The present invention also provides a manufacturing method of a displaydevice including a plurality of TFTs 30 arranged on the substrate 2 tobe processed in a manner to form a matrix, comprising the step offorming a plurality of semiconductor layers 32 for forming a pluralityof TFTs 30 on the substrate 2 to be processed, the step of laminatingthe silicon oxide layer 36 a on the semiconductor device 32, the step ofsupplying into a plasma processing chamber (chamber 11) at least threekinds of gases including an organometallic compound gas (TMA gas), anoxidizing gas, and a rare gas such that the percentage of the partialpressure of the rare gas (Pr) is not smaller than 85%, i.e.,85%≦Pr<100%, and the step of generating a plasma within the plasmaprocessing chamber so as to permit the organometallic compound gas andthe oxidizing gas to be decomposed by the plasma, thereby laminating analuminum oxide layer (Al₂O₃ film) 36 b providing a metal oxide film onthe silicon oxide layer 36 a. It follows that, according to themanufacturing method of the display device defined in the presentinvention, it is possible to form an insulating film, which has a highdielectric constant and is low in oxygen deficiency, easily, and at alow cost. Also, the manufacturing method of the display device definedin the present invention makes it possible to decrease the thickness ofthe insulating film. According to the manufacturing method of thedisplay device, the electron density within the plasma processingchamber can be markedly higher than that in the conventional method,with the result that the decomposition of the organometallic compoundgas and the oxidizing gas is promoted.

Further, the manufacturing method of the semi-conductor device accordingto the present invention comprises the step of forming the semiconductorlayer 32 in at least a part on the surface of the substrate 2 to beprocessed, the step of laminating the silicon oxide layer (SiO₂ layer)36 a on the semiconductor layer 32, the step of supplying into a plasmaprocessing chamber (chamber 11) at least three kinds of gases includingan organometallic compound gas (TMA gas), an oxidizing gas, and ahydrogen gas, and the step of generating a plasma within the plasmaprocessing chamber so as to permit the organometallic compound gas andthe oxidizing gas to be decomposed by the plasma, thereby laminating analuminum oxide layer (Al₂O₃ film) 36 b providing a metal oxide film onthe silicon oxide layer 36 a. It follows that, according to themanufacturing method of the semiconductor device outlined above, it ispossible to form an insulating film, which has a high dielectricconstant and is low in oxygen deficiency, easily, and at a low cost.Also, the manufacturing method of the semiconductor device defined inthe present invention makes it possible to decrease the thickness of theinsulating film. According to the manufacturing method of thesemi-conductor device, a reaction takes place between the hydrogen gasand the oxidizing gas, producing oxygen atoms efficiently.

The manufacturing method of the semiconductor device can be employed formanufacturing a semi-conductor device such as a thin film transistor(TFT) of a metal oxide semiconductor device (MOS device).

Still further, the present invention provides a manufacturing method ofa display device including a plurality of TFTs 30 arranged on thesubstrate 2 to be processed in a manner to form a matrix, comprising thestep of forming a plurality of semiconductor layers 32 for forming aplurality of TFTs 30 on the substrate 2 to be processed, the step oflaminating the silicon oxide layer 36 a on the semiconductor device 32,the step of supplying into a plasma processing chamber (chamber 11) atleast three kinds of gases including an organometallic compound gas (TMAgas), an oxidizing gas, and a hydrogen gas, and the step of generating aplasma within the plasma processing chamber so as to permit theorganometallic compound gas, the oxidizing gas, and the hydrogen gas tobe decomposed by the plasma, thereby laminating an aluminum oxide layer(Al₂O₃ film) 36 b providing a metal oxide film on the silicon oxidelayer 36 a. It follows that, according to the manufacturing method ofthe display device, it is possible to form an insulating film, which hasa high dielectric constant and is low in oxygen deficiency, easily, andat a low cost. Also, the manufacturing method of the display devicedefined in the present invention makes it possible to decrease thethickness of the insulating film.

Incidentally, in each of the manufacturing method of the semiconductordevice and the manufacturing method of the display device describedabove, it is desirable to laminate the silicon oxide layer having athickness of at least 2 nm. In this case, the dielectric constant of thefilm can be increased satisfactorily. According to the manufacturingmethod of the display device, the electron density within the plasmaprocessing chamber can be markedly higher than that in the conventionalmethod, with the result that the decomposition of the organometalliccompound gas and the oxidizing gas is promoted.

The manufacturing method of the display device can be employed formanufacturing a display device such as a liquid crystal display device,an organic EL display device, or an inorganic EL display device.

Also, the metal oxide film for forming the gate insulating film 36 isnot limited to an aluminum oxide film. Further, the metal oxide filmneed not be formed in a manner to overlap completely with the siliconoxide layer 36 a. Still further, the forming region of the metal oxidefilm can be selected optionally.

The technical scope of the present invention is not limited to thespecific embodiments described above. Of course, the present inventioncan be modified in various fashions within the technical scope of thepresent invention.

According to the present invention, it is possible to obtain afilm-forming method that permits forming a film low in the oxygendeficiency easily at a low cost, to obtain a method of manufacturing asemiconductor device, to obtain a semiconductor device, to obtain amethod of manufacturing a display device, and to obtain a displaydevice.

1. A film-forming method comprising: supplying into a plasma processingchamber at least three kinds of gases including a silicon compound gas,an oxidizing gas, and a rare gas, the percentage of the partial pressureof the rare gas (Pr) based on the total pressure being not smaller than85%, i.e., 85% ≦Pr<100%; and generating a plasma within the plasmaprocessing chamber so as to form a film of silicon oxide on a substrateto be processed, wherein the silicon compound gas is provided by asilane gas, and the oxidizing gas includes at least one selected fromthe group consisting of an oxygen gas and an ozone gas.
 2. Thefilm-forming method according to claim 1, wherein the plasma generatedwithin the plasma processing chamber is a surface wave plasma.